clocksource: make clocksource watchdog cycle through online CPUs

This way it checks if the clocks are synchronized between CPUs too.
This might be able to detect slowly drifting TSCs which only
go wrong over longer time.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7f60097d443a6258b2044a37b5d23f0d4656aaca..912156dd600555a2dd6be6861a80de577b3c9947 100644 (file)
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -141,8 +141,16 @@ static void clocksource_watchdog(unsigned long data)
        }
 
        if (!list_empty(&watchdog_list)) {
-               __mod_timer(&watchdog_timer,
-                           watchdog_timer.expires + WATCHDOG_INTERVAL);
+               /*
+                * Cycle through CPUs to check if the CPUs stay
+                * synchronized to each other.
+                */
+               int next_cpu = next_cpu(raw_smp_processor_id(), cpu_online_map);
+
+               if (next_cpu >= NR_CPUS)
+                       next_cpu = first_cpu(cpu_online_map);
+               watchdog_timer.expires += WATCHDOG_INTERVAL;
+               add_timer_on(&watchdog_timer, next_cpu);
        }
        spin_unlock(&watchdog_lock);
 }
@@ -164,7 +172,8 @@ static void clocksource_check_watchdog(struct clocksource *cs)
                if (!started && watchdog) {
                        watchdog_last = watchdog->read();
                        watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
-                       add_timer(&watchdog_timer);
+                       add_timer_on(&watchdog_timer,
+                                    first_cpu(cpu_online_map));
                }
        } else {
                if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
@@ -185,7 +194,8 @@ static void clocksource_check_watchdog(struct clocksource *cs)
                                watchdog_last = watchdog->read();
                                watchdog_timer.expires =
                                        jiffies + WATCHDOG_INTERVAL;
-                               add_timer(&watchdog_timer);
+                               add_timer_on(&watchdog_timer,
+                                            first_cpu(cpu_online_map));
                        }
                }
        }